1. Field of the Invention
The present invention relates to speed change control systems of an automatic transmission, and more particularly to the speed change control systems of a type that allows the transmission to exhibit a higher speed change response (viz., a rapid operation response to a speed change instruction) when the vehicle is running at a very slow speed inducing a difficulty in accurately detecting the vehicle speed.
2. Description of the Related Art
As is known, when a motor vehicle runs at a very low speed, it is practically impossible or at least difficult to accurately detect the vehicle speed and/or the gear ratio of the automatic transmission, which are needed for appropriately controlling operation of the automatic transmission.
In order to compensate a delayed response of speed change inevitably exhibited by an automatic transmission at the time when the motor vehicle runs at such very slow speed, Japanese Laid-open Patent Application (tokkai) 2002-089674 discloses a unique technique. In the technique, a command hydraulic pressure of a hydraulic system of the transmission is increased at a certain increasing rate or stepwise at the time when a speed change is carried out under the very low speed running of the vehicle. With such increase of the command hydraulic pressure, the speed change of the automatic transmission is effected quickly.